1. Field of the Invention
This invention relates to gas lift apparatus and more particularly to side pocket mandrels for use in gas lift wells.
2. Description of the Prior Art
Side pocket mandrels have long been used in the industry to house well flow control devices, such as valves. These mandrels are referred to as "side pocket" because the valve is housed in a valve pocket section that is offset from the main bore diameter. By having the valve pocket section offset in the side pocket, tools traveling up and down the hole are less likely to accidentally strike the valve. A tool striking the valve could damage or otherwise render it inoperative. The damaged valve would then have to be replaced, an expensive and time consuming process during which the well would not be producing.
Modem side pocket mandrels house the valve in a side pocket section, to further protect the valve and prevent passing tools from damaging the valve. The side pocket section has a small hole in its top to allow appropriate tools, known as kickover tools, to enter the housing to interact with the valve.
Tools used to insert, remove or otherwise interact with the valves in the side pocket mandrels are referred to as "kickover" tools. Kickover tools must be properly rotationally oriented in the flowbore to be activated for entrance into the side pocket section. To orient the kickover tools, the upper end of the mandrel traditionally has an orienting sleeve that snugly fits inside of the mandrel. This sleeve is typically provided with a pair of guide surfaces that are generally helical in shape, leading from a point at the lower end of the sleeve upwardly to the lower end of a longitudinally-aligned orienting slot. This sleeve is generally cylindrical in shape, similar to the upper end of the mandrel, and fits snugly therein. In some cases, the slot in the sleeve may pass completely through the longitudinal length of the sleeve. In other mandrels, the slot may be provided with an end or shoulder, and in some cases this shoulder completely blocks the slot. Such a shoulder at the upper end of the slot is utilized in activating a kickover tool after it has first been oriented. The slot must be long enough so that the kickover tool can be kept properly aligned while the entire tool is pulled up past the opening to the side pocket section, and to maintain alignment of the kickover tool once activated and subsequently lowered to insert the kickover tool into the side pocket section.
Kickover tools of the orienting type are provided with an orienting key sufficiently narrow to enter the orienting slot in the orienting sleeve and have an abrupt upwardly facing shoulder thereon. When this abrupt shoulder engages the orienting sleeve, it will follow one of the guide surfaces causing the kickover tool to rotate about its longitudinal axis until the key becomes aligned with and enters the slot, thus orienting the kickover tool with respect to the side pocket mandrel, i.e., positioning the kickover tool for insertion into the entrance of the side pocket section of the side pocket mandrel. In some case, as where wireline equipment is used, the same abrupt shoulder of the orienting key also engages the shoulder in the slot, and further movement of the kickover tool causes it to be activated such that a portion thereof is shifted laterally into alignment with the entrance of the side pocket section of the side pocket mandrel.
In the prior art, the orienting slot is always wholly contained within the orienting sleeve, and the interior wall of the outer mandrel housing is uniformly smooth. The orienting sleeve is placed within the outer mandrel housing during construction of the side pocket mandrel. The sleeve must be long enough to provide a slot of sufficient length to allow the kickover tool to be fully activated and vertically positioned with respect to the side pocket section. That is, not only must the kickover tool be properly aligned, it must also be moved upward sufficiently so that the lower end of the kickover tool can enter the side pocket section.
During construction of the prior art side pocket mandrels, after the orienting sleeve is inserted and positioned inside the outer mandrel housing, the sleeve is welded to the interior wall of the outer mandrel housing, and the mandrel is welded shut, sealing the sleeve inside the outer mandrel housing.
Even though the sleeve fits snugly inside the outer mandrel housing, where the surfaces of the two parts meet creates suitable locations for crevice corrosion. Such corrosion can lead to mechanical failure.
Another problem with prior art side pocket mandrels is that the orienting sleeve can sometimes become detached from the walls of the mandrel, due to corrosion of its welds, the force of a tool striking it, or a combination of the two. When this happens, the orienting sleeve can become misaligned, or travel downhole, and not only must the side pocket mandrel be replaced, the orienting sleeve must sometimes be fished out of the hole.
As the side pocket mandrel is part of the production string, it is imperative that the side pocket mandrel not mechanically fail or have to be replaced, else production will have to be stopped while the entire production string is pulled and the mandrel replaced. Therefore, it is an object of the present invention to provide a side pocket mandrel which has less area for crevice corrosion present and is less prone to breakage.